The pion pole in hard exclusive vector-meson leptoproduction

Goloskokov, S. V.; Kroll, P.

doi:10.1140/epja/i2014-14146-2

Cited by 49 publications

(78 citation statements)

References 73 publications

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“…The measured values are in good agreement with the pQCD-inspired phenomenological "GK model" calculations, 3 in which the unnatural-parity contributions due to pion exchange are included. It was based on a model which describes the deeply virtual Compton scattering rather well.…”

Section: Resultssupporting

confidence: 80%

Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES

Marukyan

2016

Int. J. Mod. Phys. Conf. Ser.

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Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied at HERMES in the kinematic region of Q 2 > 1.0 GeV 2 , 3.0 GeV < W < 6.3 GeV, and −t < 0.2 GeV 2 . The data were accumulated during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beams at HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio shows that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are derived and presented in projections of Q 2 or −t . Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ω production by longitudinal and transverse virtual photons is determined for the first time. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions.

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Section: Resultssupporting

confidence: 80%

Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES

Marukyan

2016

Int. J. Mod. Phys. Conf. Ser.

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“…The GPDs parametrized in the GK model were used in calculations of deeply virtual Compton scattering (DVCS) amplitudes, which led to good agreement with most DVCS measurements over a wide kinematic range [10]. In the most recent version of the model, the γ * πω vertex function in the one-pion-exchange contribution is identified with the πω transition form factor [11]. Its magnitude is determined in a model-dependent way, while its unknown sign may be determined from comparisons with experimental data on spin asymmetries in hard exclusive leptoproduction.…”

Section: Introductionmentioning

confidence: 99%

Transverse-target-spin asymmetry in exclusive $$\omega $$-meson electroproduction

et al. 2015

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Hard exclusive electroproduction of ω mesons is studied with the HERMES spectrometer at the DESY laboratory by scattering 27.6 GeV positron and electron beams 123 600 Page 2 of 8 Eur. Phys. J. C (2015) 75 :600 off a transversely polarized hydrogen target. The amplitudes of five azimuthal modulations of the single-spin asymmetry of the cross section with respect to the transverse proton polarization are measured. They are determined in the entire kinematic region as well as for two bins in photon virtuality and momentum transfer to the nucleon. Also, a separation of asymmetry amplitudes into longitudinal and transverse components is done. These results are compared to a phenomenological model that includes the pion pole contribution. Within this model, the data favor a positive πω transition form factor.

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“…This can be understood by considering the different contributions to exclusive omega production. The pion-pole contribution is seen to be substantial [17]. For the NPE amplitudes, the dominant contribution comes from gluons and sea quarks, which are the same for protons and neutrons, while the valence-quark contribution is different.…”

Section: Dependences Of Sdmes On Q 2 and −T And Comparison To A Phenomentioning

confidence: 85%

“…The GK model also applies successfully to the description of deeply virtual Compton scattering [16]. The results of the most recent variant of the GK model, in which the unnatural-parity contributions due to pion exchange are included to describe exclusive ω leptoproduction [17], will be compared in this paper to the HERMES proton data in terms of SDMEs and certain combinations of them.…”

Section: Introductionmentioning

confidence: 99%

Spin density matrix elements in exclusive $$\omega $$ ω electroproduction on $$^1$$ 1 H and $$^2$$ 2 H targets at 27.5 GeV beam energy

et al. 2014

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Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q 2 > 1.0 GeV 2 , 3.0 GeV < W < 6.3 GeV, and −t < 0.2 GeV 2 . Results on the angular distribution of the ω meson, including its decay products, are presented. The data were accumulated with the HER-MES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio reveals that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are presented in projections of Q 2 or −t . Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parityexchange amplitudes is found and the phase shift between those amplitudes that describe transverse ω production by longitudinal and transverse virtual photons, γ * L → ω T and γ * T → ω T , is determined for the first time. A hierarchy of helicity amplitudes is established, which mainly means that the unnatural-parity-exchange amplitude describing the γ * T → ω T transition dominates over the two natural-parityexchange amplitudes describing the γ * L → ω L and γ * T → ω T transitions, with the latter two being of similar magnitude. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions, which are of unnatural parity.

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The pion pole in hard exclusive vector-meson leptoproduction

Cited by 49 publications

References 73 publications

Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES

Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES

Transverse-target-spin asymmetry in exclusive $$\omega $$-meson electroproduction

Spin density matrix elements in exclusive $$\omega $$ ω electroproduction on $$^1$$ 1 H and $$^2$$ 2 H targets at 27.5 GeV beam energy

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